The concept of resolved motion for controlling an articulated arm is known and has been practiced for some time.
U.S. Pat. No. 5,062,755 issued Nov. 5, 1991 to Lawrence et al discloses a preferred system of resolved motion control wherein the velocity in any given direction (regardless of the position of the end point, i.e., radius of the end point) is dependent on the amount of displacement of the manual controller in that direction so that the movement of the manual controller in the direction of intended movement of the end point results in movement of the end point in that direction. The disclosure of this patent is incorporated herein by reference.
It will be apparent that controlling the movement of the end point in this manner is extremely helpful and facilitates accurate movement of the end point under the control of the operator. It will also be apparent that at the very extremities of arm movement, i.e. near a singularity, it may be impossible for the end point to move along a desired path at the desired speed, however for practical purposes throughout substantially the whole workspace of the arm, i.e. positions of the end point within a predefined workspace (that normally will include substantially the whole workspace), controls may be implemented so that movement of the controller (joystick) in a given direction results in movement of the end point in that given direction at a velocity corresponding to the amount of displacement of the controller or joystick.
It will be apparent that to ensure movement of the end point in the direction of movement of the joystick requires that the same displacement of the joystick or hand controller in any one of the x, y or z directions generates the same speed of the end point in the corresponding x, y or z direction. Thus the maximum speed of the end point is then set by the maximum speed achievable in the work space by the slowest component of movement of the end point in the work space in which the control is to so operate. Reducing the size of the work space in which the above relationship applies so that the end point does not approach singularities or other areas where velocity is severely restricted (e.g. when the endpoint approaches the z axis the velocity of the end point in the y direction approaches zero) results in the maximum cartesian velocity in slowest direction being increased.
In some cases it may be also desirable to operate in one or more directions at a speed such that it would be impossible to maintain the direction and speed relationship between joystick or hand controller movement and end point movement. For example, it may be desirable to swing the arm at a relatively fast rate without movement of the joystick precisely corresponding to the direction (and speed) of movement of end point, i.e. permitting maximum speed of the end point to be based on the physical capability of the arm and its actuators for the particular location and desired direction of movement where movements of the end point need not be precisely controlled, but prior to the present invention no such means has been available.